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Chapter 3: Movement and the Image or Centrally Excited Sensation
Margaret Floy Washburn
IN the last chapter we found reason for thinking that a stimulus produces an effect on consciousness when it initiates a motor response which is partly checked in its execution by a process of inhibition, through the influence of an antagonistic motor response. The conscious process that is thus directly occasioned by the action of an outside stimulus is called a 'sensation,' and may be further distinguished as a 'peripherally excited sensation,' to denote the difference between it and a centrally excited sensation or image. For we can get, as conscious experiences, sensations not only from outside stimuli, but by the processes which are commonly known as 'memory' and 'imagination.' Not only can I see red when red light is acting on my eyes, but I can call up a mental image of red, and even, with fair accuracy, images of a whole series of different shades and tones of red. I can not only hear the tones of a violin playing the "Prize Song" from the Meistersinger when the violinist is actually before me (or the phonograph is actually running), but I can sit here in my study, with no actual sound stimuli acting on my ears save the voices of the children across the street, and hear the tones of the violin through the entire air. The very important question now confronts us as to whether these images or centrally excited sensations are each one of them dependent on an incipient motor process, as the corresponding sensations would be if outside stimuli were acting.
A fact clear to any observation is that there often intervenes, between the giving of a stimulus and the making of a movement that an outsider can see, a long interval. A man is sitting in his business office. To him there enters an acquaintance and
( 28) asks him to write a check for one hundred dollars. The man of business says nothing, and makes no visible movement for a considerable interval of time. His friend knows very well, however, that the request has been heard and is being pondered, and waits patiently. At the end of a certain period, the business man draws his check-book and his pen to him and carries out the request. He responds to the original stimulus by making the same movements which he might appropriately have made to it at once: but during the interval between stimulus and response. he will report from introspection, a train of processes has passed through his consciousness which had no outside stimulus: which belonged to the class of centrally rather than peripherally initiated conscious processes. He may have heard in memory the words of another friend urging the claims of the cause to which lie is asked to give; he may have had a mental picture of some scene from his past.
Now, it would be quite possible to hold (d) that while these conscious processes are, taken all together, the whole series of them, caused by the delay in responding to the original outside stimulus, and thus conditioned by the initiation of the final motor response, the several and individual centrally excited processes, images, or thoughts, that filled up the interval were not, each of them, dependent on an initiated motor response of its own. On the other hand, I think a very good case can be made out for the hypothesis (b) that each of these centrally excited processes, thoughts, or images, is dependent on its own special motor response. If the first view (a) is maintained, we should suppose that the energy of the stimulus S, not finding full discharge into the motor pathways of the response. passes directly through a series of sensory centres and finally, by this indirect route, finds its way back into the motor outlet which by the direct route was not fully open. As the nervous process traverses each of the series of sensory centres, there occurs, it would be held, a centrally excited conscious process in quality like the sensation which the centre in question would mediate if it were excited by an external stimulus. To take a simple ex-
(29) -ample: the words, 'I promised my wife to give this money,' may pass through the mind of the man who sits silently pondering between the request for the money and the writing of the check. According to hypothesis (a), the energy of the stimulus (the request for the money) passes directly through a series of auditory sensory centres, and the accompaniment in consciousness is the mental hearing of the words in question. The implication of this view is that every sensory centre may have its functioning accompanied by consciousness under two wholly unlike physiological conditions. The first condition is when the energy of an outside stimulus reaches the centre. As we have seen, it appears probable that in such a case consciousness results only when the motor response is partly but not fully produced; only when excitation is partly balanced by inhibition. The second condition is when energy travels to the sensory centre directly from another sensory centre. But if the mere passage of the nervous process from one sensory centre to another is sufficient to call up a conscious process; if, that is, the traversing of a sensory centre by a nervous process coming from another sensory centre and on its way to a third is sufficient to bring an 'image' into consciousness, why is not the passage of the nervous process through a sensory centre on its way to a free motor outlet sufficient to cause consciousness in the case of the peripherally excited process' Yet we have noted the probability that the traversing of a sensory pathway by the nervous process is unaccompanied by consciousness when the motor pathway is free. On hypothesis a, then, the conditions for consciousness produced by outside stimulation, on the one hand, and the conscious processes, 'centrally excited,' involved in memory and imagination, on the other hand, would be quite unlike: the former would demand not merely the traversing of a sensory centre by a nervous current, but the partial inhibition of a motor discharge: the latter would demand merely the passage of the nervous current through the sensory centre from another centre.
Other arguments against hypothesis a will present them-
( 30)
-selves later on. Hypothesis b, that each of the centrally excited processes which make up a train of images or thoughts has its own special motor response upon whose initiation it depends, may now be further developed.
Suppose that a certain motor pathway, M, has at various times in the past been excited by energy reaching it from two different sensory pathways, S and S'. And suppose that in a given case energy from S reaches it, the effect of which is partly compensated by an inhibition from some antagonistic centre. M will then be in the kind of incomplete excitation which according to the conclusion of our last chapter is accompanied by consciousness of the sensation S. But whatever reason there may he for thinking that a process, accompanied by consciousness, is set up in S by the incipient excitation of M, would appear to hold also for the setting up of a process in S', a centre which is not now receiving any excitation from outside, but which has formerly, under the influence of outside excitation, discharged into M. The very same process which, on our hypothesis, when added to the effect of an outside stimulus makes that effect conscious, will, when it occurs in a sensory centre that is not being externally excited, be accompanied by the type of consciousness that we call 'centrally excited,' the consciousness that occurs in mental images and thoughts. When ever a motor pathway is at the same time excited by a sensory pathway and partially inhibited by an antagonistic motor excitation, a process occurs in all sensory pathways connected with the motor pathway by low synaptic resistances, including the sensory pathway that is exciting the motor pathway in question. This process is accompanied by consciousness. When it occurs in a sensory pathway that is being excited by an outside stimulus, it gives rise to the type of consciousness that we call a peripherally excited sensation. When it occurs in a sensory pathway that has no out-
(31) -side excitation, it gives rise to the type of consciousness that we call a centrally excited sensation or a mental image.[1]
How, under this hypothesis, can we explain the occurrence of a train of images or centrally excited processes, each one calling up the next? During the period between the getting of a stimulus to action and the carrying out of the action, a man's thoughts drift from one idea to another: he may in thirty seconds or so have a long train of conscious processes without any external stimulus. In the psychological laboratory, we ask students to take a certain word as a starting-point, and to introspect, without controlling, the images which follow one another through their minds.
On the theory which we are developing, such trains of centrally excited processes depend on the type of movement associations which we have called 'successive movement systems.' Take as an example the case of learning a series of nonsense syllables which are visually presented, printed or written, before one. For the sake of simplicity let us neglect the part played by auditory sensations, peripherally or centrally excited, and consider the process of pronouncing the syllables, as one looks at them, simply as a motor process whose stimulus is visual. In reading the series through we have a succession of visual stimuli, each followed by its proper motor response. Now, as the series is repeatedly read, each motor process comes to have two stimuli: the original visual one, the sight of the printed or written syllable, and also the kinesthetic 'feel' of pronouncing the syllable just preceding. The more thoroughly the series is learned, the more the kinesthetic stimulus becomes sufficient by itself, without the visual one, to set off the movement. When the series is thoroughly learned, one can say it 'without book,' that is, without any visual stimuli at all. If, however, in reciting a series of syllables without the copy before
(32) one, there is a delay; if some inhibition arises, then one may recall the look of the missing syllable, more or less accurately; that is, delay in the discharge of a motor centre produces, in the sensory centre which formerly discharged into it, that process upon which there is based consciousness of the sensation, centrally excited, which would be peripherally excited if an actual stimulus were acting on the sensory centre and its motor response were delayed.
This is what happens, we may suppose, when the series of syllables is actually being recited; that is, when the movements of articulation are being fully performed. If a hitch comes in the recitation, a mental image of the look of the syllables may be recalled. What, now, takes place when the series is not recited aloud, or even whispered, but merely 'run through' mentally% The thoughts or images which we have fancied to occur in the mind of the man deliberating whether he shall write a check do not take place, each of them, in the course of a series of actual movements that are visible externally. But nevertheless, — and this is a crucial assumption for our whole hypothesis, — there probably are, going on in his muscles, slight actual contractions. So when we mentally run over a series of nonsense syllables that we have learned by heart, it must be supposed that slight actual movements of the articulatory muscles do occur. Introspection furnishes some evidence of the fact. Try, for instance, the following test: pronounce aloud or in a whisper the letter ' b' successively twenty-five times, and as you pronounce it try, absolutely simultaneously, to think of each of the other letters of the alphabet. You will find that, whether you think of them in auditory or visual terms, whether you mentally bear them or mentally see them, you have to slip them in between your pronunciations of 'b': the sequence of events in your consciousness has to be 'h a,' 'b c,' 'b d,' and soon. Or try James's old experiment of holding the mouth open and thinking of the word 'bubble.' In this case, to my introspection, the auditory image is impossible, but I can form pretty well a visual image of the word. In general,
Chapter 3: Movement and the Image or Centrally Excited Sensation
Margaret Floy Washburn
IN the last chapter we found reason for thinking that a stimulus produces an effect on consciousness when it initiates a motor response which is partly checked in its execution by a process of inhibition, through the influence of an antagonistic motor response. The conscious process that is thus directly occasioned by the action of an outside stimulus is called a 'sensation,' and may be further distinguished as a 'peripherally excited sensation,' to denote the difference between it and a centrally excited sensation or image. For we can get, as conscious experiences, sensations not only from outside stimuli, but by the processes which are commonly known as 'memory' and 'imagination.' Not only can I see red when red light is acting on my eyes, but I can call up a mental image of red, and even, with fair accuracy, images of a whole series of different shades and tones of red. I can not only hear the tones of a violin playing the "Prize Song" from the Meistersinger when the violinist is actually before me (or the phonograph is actually running), but I can sit here in my study, with no actual sound stimuli acting on my ears save the voices of the children across the street, and hear the tones of the violin through the entire air. The very important question now confronts us as to whether these images or centrally excited sensations are each one of them dependent on an incipient motor process, as the corresponding sensations would be if outside stimuli were acting.
A fact clear to any observation is that there often intervenes, between the giving of a stimulus and the making of a movement that an outsider can see, a long interval. A man is sitting in his business office. To him there enters an acquaintance and
( 28) asks him to write a check for one hundred dollars. The man of business says nothing, and makes no visible movement for a considerable interval of time. His friend knows very well, however, that the request has been heard and is being pondered, and waits patiently. At the end of a certain period, the business man draws his check-book and his pen to him and carries out the request. He responds to the original stimulus by making the same movements which he might appropriately have made to it at once: but during the interval between stimulus and response. he will report from introspection, a train of processes has passed through his consciousness which had no outside stimulus: which belonged to the class of centrally rather than peripherally initiated conscious processes. He may have heard in memory the words of another friend urging the claims of the cause to which lie is asked to give; he may have had a mental picture of some scene from his past.
Now, it would be quite possible to hold (d) that while these conscious processes are, taken all together, the whole series of them, caused by the delay in responding to the original outside stimulus, and thus conditioned by the initiation of the final motor response, the several and individual centrally excited processes, images, or thoughts, that filled up the interval were not, each of them, dependent on an initiated motor response of its own. On the other hand, I think a very good case can be made out for the hypothesis (b) that each of these centrally excited processes, thoughts, or images, is dependent on its own special motor response. If the first view (a) is maintained, we should suppose that the energy of the stimulus S, not finding full discharge into the motor pathways of the response. passes directly through a series of sensory centres and finally, by this indirect route, finds its way back into the motor outlet which by the direct route was not fully open. As the nervous process traverses each of the series of sensory centres, there occurs, it would be held, a centrally excited conscious process in quality like the sensation which the centre in question would mediate if it were excited by an external stimulus. To take a simple ex-
(29) -ample: the words, 'I promised my wife to give this money,' may pass through the mind of the man who sits silently pondering between the request for the money and the writing of the check. According to hypothesis (a), the energy of the stimulus (the request for the money) passes directly through a series of auditory sensory centres, and the accompaniment in consciousness is the mental hearing of the words in question. The implication of this view is that every sensory centre may have its functioning accompanied by consciousness under two wholly unlike physiological conditions. The first condition is when the energy of an outside stimulus reaches the centre. As we have seen, it appears probable that in such a case consciousness results only when the motor response is partly but not fully produced; only when excitation is partly balanced by inhibition. The second condition is when energy travels to the sensory centre directly from another sensory centre. But if the mere passage of the nervous process from one sensory centre to another is sufficient to call up a conscious process; if, that is, the traversing of a sensory centre by a nervous process coming from another sensory centre and on its way to a third is sufficient to bring an 'image' into consciousness, why is not the passage of the nervous process through a sensory centre on its way to a free motor outlet sufficient to cause consciousness in the case of the peripherally excited process' Yet we have noted the probability that the traversing of a sensory pathway by the nervous process is unaccompanied by consciousness when the motor pathway is free. On hypothesis a, then, the conditions for consciousness produced by outside stimulation, on the one hand, and the conscious processes, 'centrally excited,' involved in memory and imagination, on the other hand, would be quite unlike: the former would demand not merely the traversing of a sensory centre by a nervous current, but the partial inhibition of a motor discharge: the latter would demand merely the passage of the nervous current through the sensory centre from another centre.
Other arguments against hypothesis a will present them-
( 30)
-selves later on. Hypothesis b, that each of the centrally excited processes which make up a train of images or thoughts has its own special motor response upon whose initiation it depends, may now be further developed.
Suppose that a certain motor pathway, M, has at various times in the past been excited by energy reaching it from two different sensory pathways, S and S'. And suppose that in a given case energy from S reaches it, the effect of which is partly compensated by an inhibition from some antagonistic centre. M will then be in the kind of incomplete excitation which according to the conclusion of our last chapter is accompanied by consciousness of the sensation S. But whatever reason there may he for thinking that a process, accompanied by consciousness, is set up in S by the incipient excitation of M, would appear to hold also for the setting up of a process in S', a centre which is not now receiving any excitation from outside, but which has formerly, under the influence of outside excitation, discharged into M. The very same process which, on our hypothesis, when added to the effect of an outside stimulus makes that effect conscious, will, when it occurs in a sensory centre that is not being externally excited, be accompanied by the type of consciousness that we call 'centrally excited,' the consciousness that occurs in mental images and thoughts. When ever a motor pathway is at the same time excited by a sensory pathway and partially inhibited by an antagonistic motor excitation, a process occurs in all sensory pathways connected with the motor pathway by low synaptic resistances, including the sensory pathway that is exciting the motor pathway in question. This process is accompanied by consciousness. When it occurs in a sensory pathway that is being excited by an outside stimulus, it gives rise to the type of consciousness that we call a peripherally excited sensation. When it occurs in a sensory pathway that has no out-
(31) -side excitation, it gives rise to the type of consciousness that we call a centrally excited sensation or a mental image.[1]
How, under this hypothesis, can we explain the occurrence of a train of images or centrally excited processes, each one calling up the next? During the period between the getting of a stimulus to action and the carrying out of the action, a man's thoughts drift from one idea to another: he may in thirty seconds or so have a long train of conscious processes without any external stimulus. In the psychological laboratory, we ask students to take a certain word as a starting-point, and to introspect, without controlling, the images which follow one another through their minds.
On the theory which we are developing, such trains of centrally excited processes depend on the type of movement associations which we have called 'successive movement systems.' Take as an example the case of learning a series of nonsense syllables which are visually presented, printed or written, before one. For the sake of simplicity let us neglect the part played by auditory sensations, peripherally or centrally excited, and consider the process of pronouncing the syllables, as one looks at them, simply as a motor process whose stimulus is visual. In reading the series through we have a succession of visual stimuli, each followed by its proper motor response. Now, as the series is repeatedly read, each motor process comes to have two stimuli: the original visual one, the sight of the printed or written syllable, and also the kinesthetic 'feel' of pronouncing the syllable just preceding. The more thoroughly the series is learned, the more the kinesthetic stimulus becomes sufficient by itself, without the visual one, to set off the movement. When the series is thoroughly learned, one can say it 'without book,' that is, without any visual stimuli at all. If, however, in reciting a series of syllables without the copy before
(32) one, there is a delay; if some inhibition arises, then one may recall the look of the missing syllable, more or less accurately; that is, delay in the discharge of a motor centre produces, in the sensory centre which formerly discharged into it, that process upon which there is based consciousness of the sensation, centrally excited, which would be peripherally excited if an actual stimulus were acting on the sensory centre and its motor response were delayed.
This is what happens, we may suppose, when the series of syllables is actually being recited; that is, when the movements of articulation are being fully performed. If a hitch comes in the recitation, a mental image of the look of the syllables may be recalled. What, now, takes place when the series is not recited aloud, or even whispered, but merely 'run through' mentally% The thoughts or images which we have fancied to occur in the mind of the man deliberating whether he shall write a check do not take place, each of them, in the course of a series of actual movements that are visible externally. But nevertheless, — and this is a crucial assumption for our whole hypothesis, — there probably are, going on in his muscles, slight actual contractions. So when we mentally run over a series of nonsense syllables that we have learned by heart, it must be supposed that slight actual movements of the articulatory muscles do occur. Introspection furnishes some evidence of the fact. Try, for instance, the following test: pronounce aloud or in a whisper the letter ' b' successively twenty-five times, and as you pronounce it try, absolutely simultaneously, to think of each of the other letters of the alphabet. You will find that, whether you think of them in auditory or visual terms, whether you mentally bear them or mentally see them, you have to slip them in between your pronunciations of 'b': the sequence of events in your consciousness has to be 'h a,' 'b c,' 'b d,' and soon. Or try James's old experiment of holding the mouth open and thinking of the word 'bubble.' In this case, to my introspection, the auditory image is impossible, but I can form pretty well a visual image of the word. In general,